Dc power supply regulated by a shunt transistor whose bias voltage is varied by transistor means to stabilize load voltage

ABSTRACT

An adjustable DC power supply regulated by the combination of a voltage dropping resistor in series between the DC source and the load, a transistor shunting the load, and other transistor circuitry that monitors the load voltage while drawing very little current, and responds to any load voltage change to adjust the bias on the shunt transistor in a direction to change the current drawn by the shunt transistor and thereby to change the voltage drop across the voltage dropping resistor to oppose change in load voltage.

United States Patent Inventor Appl. No. Filed Patented Assignee DC POWERSUPPLY REGULATED BY A SHUNT TRANSISTOR WHOSE BIAS VOLTAGE IS VARIED BYTRANSISTOR MEANS TO STABILIZE LOAD VOLTAGE Primary Examiner-GeraldGoldberg Attorneys-Louis A. Miller, Louis B. Applebaum and Ernest F.Weinberger ABSTRACT: An adjustable DC power supply regulated by thecombination of a voltage dropping resistor in series between the DCsource and the load, a transistor shunting the load, and

4 Chins 4 Dn'inl other transistor circuitry that monitors the loadvoltage while US. Cl 323/22 T, drawing very little current, and respondsto any load voltage 307/297, 323/38 change to adjust the bias on theshunt transistor in a direction Int. Cl G05f 1/60 to change the currentdrawn by the shunt transistor and Field of Search 323/4, 9, thereby tochange the voltage drop across the voltage 16-22, 22 T, 7, 8, 38;307/297 dropping resistor to oppose change in load voltage.

a: /5 m T T 4 90 k F l PATENTED SEP14|97| SHEET 3 BF 3 INVENTOR. iPaBEATZ. J5me 63mm wmg m A 7 rokza gs DC POWER SUPPLY REGULATED BY A SHUNTTRANSISTOR WHOSE BIAS VOLTAGE IS VARIED BY TRANSISTOR MEANS TO STABILIZELOAD VOLTAGE BACKGROUND OF THE INVENTION 1. Field of the Invention Thepresent invention relates to electronic power supplies and moreparticularly to highly accurate adjustable regulated direct currentsupplies wherein there is included a voltage dropping resistor in seriesbetween the unregulated source and the load, and a transistor shuntingthe load to draw variable current through the voltage dropping resistorto oppose change in voltage across the load and a transistorized seriesnetwork that monitors the load voltage and operates to vary the bias ofthe shunt transistor to stabilize the load voltage while drawing currentthat is a minute percentage of the load current.

2. Description of the Prior Art In the field of regulated powersupplies, it has been the general practice to employ series connectedsupplies wherein a fault element controls or cuts off a series componentunder extreme load conditions. This inherently demand that high loadcurrents are carried by the series component. The output drop initiatesthe prevention of damage to the series component. Such devices have beenunsatisfactory in that high currents or the entire load current passesthrough a particular component producing an excessive drop, inefficientoperation, and unstable outputs.

SUMMARY OF THE INVENTION The general purpose of this invention is toprovide a highly stable and accurate variable power supply that has allthe advantages of similarly employed prior art devices and has none ofthe above described disadvantages. To attain this, the present inventionprovides a unique arrangement of circuits wherein a DC power source isconnected in series with a current-limiting resistor and the load, ashunt transistor has its emitter-collector in parallel with the load andits base connected to receive the output of a series connected constantvoltage means, which means receives said source as its input, wherebyinstability and inaccuracy are avoided.

An object of the present invention is to provide an inexpensive, highlyaccurate, simple regulated variable power supply having overloadprotection.

Another object is to provide a series-shunt regulated variable powersupply wherein only an extremely minute fraction of the load currentpasses through the series regulation circuit.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings, in which like referencenumerals designate like parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of anembodiment illustrating the principle of this invention;

FIG. 2 is a schematic wiring diagram of the embodiment shown in FIGS. 1;and

FIGS. 3 and 4 are schematics of alternate embodiments made in accordancewith the principle of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS the load 11 is equal to thealgebraic sum of the output voltage V, of theseries means 14 and theemitter-base voltage V of the shunt transistor 18. As a general rule, Vis relatively small, as for example, 0.2 to 0.5 volts compared to V,which is usually in excess of 25 volts. The series means 14 provides aconstant voltage V, at its output no matter how the input E varies sinceit includes a feedback loop as will be explained hereinafter. In theevent of a short circuit across the load, the series resistor 12 willlimit the current drawn from the DC supply 10 while only a smallfractional part thereof will flow in the series means 14 and the majorportion will flow through the shunt transistor 18.

In the illustrated embodiment of FIG. 2, the series means I4 comprisesan input shunt capacitor 21 for filtering and smoothing the DC input E Aresistor 22 connects input 13 to the collector 23 of series regulatingtransistor 24. Resistors 25 and 26 provide the base 27 bias via thecollector 28 of control amplifier transistor 29. Zener diode 30 insuresthat a relatively constant voltage is supplied at the emitter 31 oftransistor 24, which also maintains a constant voltage for transistor29. Capacitor 32 reduces the noise present at the base 33 of transistor29, which is tied to the movable arm 34 of potentiometer 35, which, witharm resistors 36 and 37, forms a voltage divider connected across theoutput of the emitter-base of transistor 24. Limiting resistor 38 andzener diode 39 provide a constant reference voltage at the emitter 40 ofcontrol amplifier transistor 29, which is relatively independent ofchanges in the output V The series constant voltage means operatesgenerally as follows: The variable output voltage V, is selected byadjusting the arm 34 of the potentiometer 35. If, however, the voltageV, should thereafter change, the voltage at the divider arm and so thebase (33) voltage at the control amplifier transistor 29 will bealtered. Since this transistor is an amplifier, this change in V, isamplified and appears directly at the base 27 of the series regulatingtransistor 24. The base voltage change effectively alters thecollector-emitter resistance and thereby compensates for the change inV, to return to the originally selected voltage.

It should be noted that this series circuit is a closed loop in that theoutput V is fed back to a series control while the shunt circuit(transistor 18) is an open loop configuration.

Referring now to the embodiment illustrated in FIG. 3, the seriesvoltage means 14 and the shunt transistor circuit are identical to thosepreviously described. Bearing in mind that the regulated output E is thesum of the series voltage V, and the base-emitter voltage V of the shunttransistor I8, it is clear that small changes in V have not beenentirely compensated, although they are of a small magnitude. In orderto provide such compensation, a second shunt circuit 41, which comprisesa transistor 42 whose emitter 43 and collector 44 are connected acrossthe load 11 via resistors 45 and 46 is provided. The base 47 isconnected to the junction between the parallel connected combination ofresistor 48 and zener diode 49. The voltage across the load E is equalto the sum of the drop V, across the zener diode 49 and the drop Vacross the resistor 48. Since V, is a reference or fixed value, than anychange in E appears entirely across the resistor 48 and therefore at thebase 47 of transistor 42, which in turn changes (amplifies) the voltageat the collector 44. This change is reflected across resistor 46 and viaresistor 50 is coupled to the base 33 of control amplifier transistor29, which in turn is reflected to the series regulator 24 to alter V, tocompensate for changes in V of the shunt transistor. (It should be notedthat in this embodiment the shunt is a closed loop in that a voltagechange therein is fed back to control V, in the series means 14.)

Considering for the moment the reference or fixed voltage at zener diode39, it is clear that this diode has passing therethrough theemitter-collector current of transistor 29, which is functionally anamplifier. Thus, as the base voltage (or V,) changes, this change isamplified and appears in the emitter-collector current which passesthrough reference diode 39. Although under ordinary conditions a zenerdiode will maintain a constant voltage, if the current therethroughchanges (depending on operating region) the voltage will be slightlyaltered, since this voltage as well as the change is in the emitter-basecircuit it amplified. It has been found that for a certain specificzener diode, a current difference from 1 to 2 milliamperes results in avoltage change from 10.00 to l0.05 volts. In order to overcome thisinherent limitation, an additional transistor 51 is inserted in serieswith emitter resistor 52 across the divider circuit. The voltage acrossresistor 52 is coupled as the fixed reference voltage to the emitter 40of control transistor 29. The junction between resistor 53 and zenerdiode 54 is tied to the base 55 of transistor 51. These two elements arealso in parallel with the divider so that the change in current throughthe zener is relatively small and the reference potential is at theemitter 56 (across resistor 52 Typical operating differences inregulation between the circuits of FIGS. 2. l and 4 are as follows:

All of these circuits can be short circuited at the output without anydamage to the components and by proper selection of the specifictransistors and diodes temperature compensation can be readilyincorporated,

lclaim:

l. A transistor regulated DC power supply which comprises:

a source of electrical energy,

a current limiting resistor,

a pair 01 iutput terminals,

a series l op circuit having therein said source, said resistor and sa 1output terminals,

a shunt transistor having its emitter electrically connectedintermediate said resistor and one of said pair of terminals and itscollector connected to the other of said pair of terminals,

an input capacitor connected across said emitter and collector of saidshunt transistor,

electrical means connecting the output of said voltage means to the baseof said shunt transistor,

a series-regulating transistor having an emitter, collector and a baseelement,

a voltage divider means having an adjustable output arm intermediate theends thereof,

a control amplifier transistor having an emitter, collector,

and a base element.

a second series loop circuit including therein said source, saidemitter, said collector of said regulating transistor and said voltagedivider means,

first electrical means connecting said adjustable arm to said base ofsaid control transistor,

a series combination of a first resistor and a zener diode connectedintermediate said emitter of said regulating transistor and saidcollector of said control amplifier transistor,

a second electrical means connecting said emitter of said controltransistor and the junction of said zener diode and said first resistor,and

third electrical means connecting said emitter of said regulatmgtransistor to said base of said shunt transistor.

2. The regulated supply accordingly to claim 1, further including:

a secondary shunt transistor having an emitter, collector and a baseelement,

an emitter resistor,

a collector resistor,

a series network including said emitter resistor said secondary shunttransistor emitter and collector, and said c]- lector resistor connectedacross said pair of output terminals,

a second series combination of a second resistor and a second zenerdiode connected intennediate said pair of output terminals and havingsaid base of said secondary shunt transistor connected to the junctionof said second resistor and zener diode, and

a coupling resistor connected intermediate said collector of saidsecondary shunt transistor and said base of said control transistor,

a second electrical means connecting said emitter of said controltransistor and the junction of said zener diode and said first resistorand third electrical means connecting said emitter of said regulatingtransistor to said base of said shunt transistor.

3. A transistor regulated DC power supply which comprises:

a source of electrical energy,

a current limiting resistor,

a pair of output terminals,

a series loop circuit having therein said source, said resistor and saidoutput terminals,

a shunt transistor having its emitter electrically connectedintermediate said resistor and one of said pair of terminals and itscollector connected to the other of said pair of terminals,

electrical means connecting the output of said voltage means to the baseof said shunt transistor,

an input capacitor connected across said emitter and collector of saidshunt transistor,

a series-regulating transistor having an emitter, collector and a baseelement,

a voltage divider means having an adjustable output arm intermediate theends thereof,

a control amplifier transistor having an emitter, collector and a baseelement,

a second series loop including therein said source, said emitter, saidcollector of said regulating transistor, and said voltage divider means,

first electrical means connecting said adjustable arm to said base ofsaid control transistor, and connecting said collector thereof to saidbase of said regulating transistor,

a reference transistor having an emitter, collector and a base element,

an emitter resistor,

a base resistor,

a reference zener diode,

second electrical means connecting in parallel across said divider meanstwo circuits, one of said circuits including in series said collector,emitter and said emitter resistor of said reference transistor, theother of said circuits including in series said base resistor and saidzener,

third electrical means connecting the junction of said reference zenerand said base resistor to said base of said reference transistor,

fourth electrical means connecting said emitters of said control andreference transistors, and

fifth electrical means connecting said emitter of said regulatingtransistor to said base of said shunt transistor.

4. The regulated @Bifictfikifi t o claim 3, further in- I cludig asecondary shunt transistor having an emitter, co llector and a baseelement, a emitter resistor,

a collector resistor,

a series network including said emitter resistor, said secon Q

1. A transistor regulated DC power supply which comprises: a source ofelectrical energy, a current limiting resistor, a pair of outputterminals, a series loop circuit having therein said source, saidresistor and said output terminals, a shunt transistor having itsemitter electrically connected intermediate said resistor and one ofsaid pair of terminals and its collector connected to the other of saidpair of terminals, an input capacitor connected across said emitter andcollector of said shunt transistor, electrical means connecting theoutput of said voltage means to the base of said shunt transistor, aseries-regulating transistor having an emitter, collector and a baseelement, a voltage divider means having an adjustable output armintermediate the ends thereof, a control aMplifier transistor having anemitter, collector, and a base element, a second series loop circuitincluding therein said source, said emitter, said collector of saidregulating transistor and said voltage divider means, first electricalmeans connecting said adjustable arm to said base of said controltransistor, a series combination of a first resistor and a zener diodeconnected intermediate said emitter of said regulating transistor andsaid collector of said control amplifier transistor, a second electricalmeans connecting said emitter of said control transistor and thejunction of said zener diode and said first resistor, and thirdelectrical means connecting said emitter of said regulating transistorto said base of said shunt transistor.
 2. The regulated supplyaccordingly to claim 1, further including: a secondary shunt transistorhaving an emitter, collector and a base element, an emitter resistor, acollector resistor, a series network including said emitter resistorsaid secondary shunt transistor emitter and collector, and saidcollector resistor connected across said pair of output terminals, asecond series combination of a second resistor and a second zener diodeconnected intermediate said pair of output terminals and having saidbase of said secondary shunt transistor connected to the junction ofsaid second resistor and zener diode, and a coupling resistor connectedintermediate said collector of said secondary shunt transistor and saidbase of said control transistor, a second electrical means connectingsaid emitter of said control transistor and the junction of said zenerdiode and said first resistor and third electrical means connecting saidemitter of said regulating transistor to said base of said shunttransistor.
 3. A transistor regulated DC power supply which comprises: asource of electrical energy, a current limiting resistor, a pair ofoutput terminals, a series loop circuit having therein said source, saidresistor and said output terminals, a shunt transistor having itsemitter electrically connected intermediate said resistor and one ofsaid pair of terminals and its collector connected to the other of saidpair of terminals, electrical means connecting the output of saidvoltage means to the base of said shunt transistor, an input capacitorconnected across said emitter and collector of said shunt transistor, aseries-regulating transistor having an emitter, collector and a baseelement, a voltage divider means having an adjustable output armintermediate the ends thereof, a control amplifier transistor having anemitter, collector and a base element, a second series loop includingtherein said source, said emitter, said collector of said regulatingtransistor, and said voltage divider means, first electrical meansconnecting said adjustable arm to said base of said control transistor,and connecting said collector thereof to said base of said regulatingtransistor, a reference transistor having an emitter, collector and abase element, an emitter resistor, a base resistor, a reference zenerdiode, second electrical means connecting in parallel across saiddivider means two circuits, one of said circuits including in seriessaid collector, emitter and said emitter resistor of said referencetransistor, the other of said circuits including in series said baseresistor and said zener, third electrical means connecting the junctionof said reference zener and said base resistor to said base of saidreference transistor, fourth electrical means connecting said emittersof said control and reference transistors, and fifth electrical meansconnecting said emitter of said regulating transistor to said base ofsaid shunt transistor.
 4. The regulated supply according to claim 3,further including: a secondary shunt transistor having an emitter,collector and a baSe element, a emitter resistor, a collector resistor,a series network including said emitter resistor, said secondary shunttransistor emitter and collector, and said collector resistor connectedacross said pair of output terminals, a second series combination of asecond resistor and a second zener diode connected intermediate saidpair of output terminals and having said base of said secondary shunttransistor connected to the junction of said second resistor and zenerdiode, and a coupling resistor connected intermediate said collector ofsaid secondary shunt transistor and said base of said controltransistor.